The present invention relates to a fuel injection timing control apparatus of a distributor injection pump for a diesel engine.
As is well known in the diesel engine field, a distributor injection pump of a diesel engine is generally adapted to advance a fuel injection timing at which the distributor injection pump distributes fuel as a rise of revolution speed of the diesel engine. In order to decrease one of emissions, oxides of nitrogen (NOx), in the exhaust from the diesel engine driven in a low or a relatively low range of engine loading most frequently used, the distributor injection pump is provided with a so-called load-sensing timer as a fuel injection timing advancing device to operate the fuel injection pump at a retarded injection timing in the low or relatively low range of engine loading more later than in a high range of engine loading, simultaneously with dropping the burning temperature of fuel in the diesel engine by the aid of an exhaust gas recirculation device ( EGR ).
Meanwhile, when operating the diesel engine at high elevations, for example higher than approximately an altitude of 1,600 m, but depending on diesel engines, where the air becomes thinner and atmospheric pressure drops, compressed air pressure tends to become lower due to a lowered density of the air, leading to a deterioration of the inflammability of fuel. Therefore, when operating in the low or relatively low range of engine loading at high elevations, the diesel engine often causes what may be called misfiring or incomplete firing due to the deterioration of the inflammability of fuel caused by the dropped compressed air pressure and the exhaust gas recirculation, in addition to the retarded fuel injection timing of the distributor injection pump by the so-called load-sensing timer, resulting in a decline of engine power which not only lowers a performance of the diesel engine operation but also makes the diesel engine produce emissions including white smoke. Moreover, the diesel engine, which essentially tends to emit smoke ( black smoke ) in the high range of engine loading at high elevations, exhausts still more smoke due to the fact that the fuel mixture tends to become overly rich in that the air becomes thinner and contains less oxygen to sustain burning.
In an attempt at overcoming this problem of the prior art distributor injection pumps, an improved fuel injection timing control device has been proposed in, for example, Japanese Utility Model Publication No. 60-8,129 issued on Mar. 20, 1985, entitled "Distributor Injection Pump". In this distributor injection pump, a fuel injection timing control device is adapted substantially to advance a fuel injection timing of the distributor injection pump by suspending the load-sensing timer in the low or relatively low range of engine loading at high elevations where atmospheric pressure drops lower than a pressure predetermined in association with the diesel engine.
One disadvantage associated with such distributor injection pump of the type which has the load-sensing timer suspended when operating in the low or relatively low range of engine loading at high elevations is that, because the distributor injection pump distributes fuel at fuel injection timing advanced depending only on a rotation speed of the diesel engine but is not compensated in accordance with engine loading, it is a bit difficult to eliminate the occurrence of misfiring or incomplete firing in the low or relatively low range of engine loading and to eliminate or control smoke emitted on burning in the high range of engine loading; the performance of diesel engine operation is possibly lowered and emission control is still difficult.
One approach to overcoming drawbacks associated with such a distributor injection pump has become known from Japanese Utility Model Unexamined Publication No. 59-157,549 laid open Oct. 23, 1984, entitled "Fuel Injection Pump" disclosed by the same applicant of this application, in which a fuel injection timing of the fuel injection pump is, when operating at high elevations where atmospheric pressure drops, advanced in the low or relatively low range of engine loading and, on the other hand, retarded in the high range of engine loading later than in the low or relatively low range of engine loading. For accomplishing this, a fuel injection timing control apparatus cooperates with a specific load-sensing timer which is so constructed as to reverse the relationship between an advance-retardation characteristic of fuel injection timing and the range of engine loading between the high and the low or relatively low elevations.